The following publications are referenced herein:    1. U.S. Pat. No. 6,257,074 to Kellerman;    2. U.S. Pat. No. 8,135,504 to Summers;    3. Armagh Observatory web page, “Cup-anemometer by Munro 1870”, viewed Apr. 8, 2013 at www.arm.ac.uk/history/instruments/Robinson-cup-anemometer.html;    4. Raymarine Inc., “Raymarine Instrument Transducer Options”, viewed May 24, 2013 at http://www.raymarine.com/view/?id=1479&collectionid=8&col=1484;    5. Garmin Stockholm AB web page, “nWind Transducer”, viewed May 24, 2013 at www.nexusmarine.se/products/marine-instruments/transducers/nwind-transducer/;    6. Olin Sailbot Robotic Sailing Team, Olin College of Engineering, Needham, Mass., USA, viewed May 23, 2013 at www.olinsailbot.com/2012/04/09/unfiltering-the-wind-sensor/;    7. Expert Group Study on Recommended Practices for Wind Turbine Testing and Evaluation (1999), “11. Wind Speed Measurement and Use of Cup Anemometry”, International Energy Agency Programme for Research and Development on Wind Energy Conversion Systems (IEA Wind), viewed Apr. 8, 2013 at www.ieawind.org/task_11/recommended_pract/11_Anemometry.pdf;    8. Airmar Technology Corporation brochure “PB200”, obtained online in PDF format on Jan. 19, 2011 and May 23, 2013 at www.airmartechnology.com/uploads/brochures/pb200.pdf;    9. Pedersen, T. F. et al. (2002). Riso National Laboratory, Technical University of Denmark. “Wind Turbine Power Performance Verification in Complex Terrain and Wind Farms”, viewed May 24, 2013 at http://orbit.dtu.dk/fedora/objects/orbit:91603/datastreams/file_7726871/content; and    10. Adolf Thies GmbH & Co. KG, “Thies Anemometer First Class Advanced” product specification sheet (May 16 2012 version), Gottingen, Germany, viewed Apr. 8, 2013 at www.ammonit.com/images/stories/download-pdfs/TestReports/en_dtwindguard_cupanemometerclass_122008.pdf.
One of the fundamental challenges with sailboat navigation is that sailors need a method of determining the headings, times and distances for their possible routes and optimal tacks. The United States of America patent by Summers (U.S. Pat. No. 8,135,504) defined a way to quickly and easily calculate these tacking results, although it works best if the tacking calculations can be continually updated with real-time wind data. Although these calculations are available worldwide in mobile apps, there are few anemometers available that can transmit wind data to mobile devices, no mounted anemometers available that are immersible if a small sailboat flips, and no anemometer that works equally accurately when heeling over while sailing.
The main sensors or anemometers for measuring wind speed are propellers, impellers in a tube, cups that move from the force of the wind, and more recent ultrasonic sensors. Wind arrows are added for sensing wind direction, or that turn the impeller into the wind. The original Robinson 4-cup anemometer was installed at the Armagh Observatory in Ireland in 1846. The cup sensor used an existing technology of the day, a mechanical clockworks to record the number of cup rotations in a time period on a rotating drum. But other than favoring 3 cups now, and replacing the drum with electronics to record and display the wind speeds, cup anemometers have been largely unchanged in over 150 years.
Handheld anemometers such as the one patented in the United States of America by Kellerman in 2001 (U.S. Pat. No. 6,257,074) are popular. This is an example of an anemometer with an impeller inside a short tube. However, handheld anemometers do not provide continuous read-outs, since they are designed to be handheld rather than mounted, and thus checked occasionally by holding them up into the wind. They typically do not include a wind direction arrow, only an impeller for wind speed. It is also very difficult on a small handheld anemometer to know if you are aiming it directly into the wind to get an accurate reading. Also, sailors need their hands free for handling ropes, sails and the tiller or wheel.
A number of styles of mounted anemometers are available, with cups, propellers or ultrasonic sensors with no moving parts. One problem is that these are generally designed to be water-resistant when upright, but not designed for use on small sailboats, which flip and could therefore submerge the anemometer mounted at the masthead. More importantly, there do not appear to be any anemometers that are invariant to tilt of the sailboat; they all become increasingly inaccurate the more a sailboat heels over while actually sailing (exactly when they are needed).
For example, Raymarine has several models of cup anemometers—Rotavecta, ST60 and TackTick—all of which use traditional half-sphere cups which face the wind less and less the more the sailboat heels over when sailing. The same appears to be true for the propeller blades on the Garmin/Nexus Wind Transducer. All 3 blades turn in the wind when their axis is horizontal, although when the sailboat heels over, one of them has to move into the wind and is not cupped to reduce wind resistance. This would be like expecting a 3-bladed propeller on a small airplane to rotate when the wind is from the side; it is only designed to catch the wind along the axis of its rotation. The Garmin/Nexus twin wind direction arrows also contain large flat surfaces that simply block the wind as they become more vertical when the sailboat heels over. Like all propeller anemometers, the Garmin/Nexus also only gives accurate wind speed after it has turned into the wind; it does not work with wind from any direction, as a cup anemometer does.
Ultrasonic anemometers have no moving parts. They transmit sounds above the range of human hearing in several different directions and measure the arrival time to infer the direction and speed of the wind. However, the sound waves are affected by air temperature and precipitation. The highly-promoted Airmar brand appears to have a response lag of 10 seconds to any wind shift—which many sailors would find too slow—because the wind data is buffered and averaged, according to a study at Olin College of Engineering. More importantly, the shape of the sensing heads can interfere with wind flow. Even when upright, this wind flow distortion can produce wind speed errors in sonic anemometers, according to the Expert Group Study on Recommended Practices for Wind Turbine Testing and Evaluation. But more importantly for sailors, since sailboats heel over when under sail, ultrasonic anemometers like the Airmar contain a thin horizontal slot for the wind to pass through. As the boat heels over, the base of the unit itself obstructs this slot. An Airmar brochure notes that the upper limit for accuracy is 30 degrees of tilt, although it does not say how much accuracy has dropped off by this point.
Those skilled in the art will know that there is a body of research particularly from assessing wind farm turbines, showing that as an anemometer tilts (or the wind approaches the anemometer on a vertical angle), the reported wind speed falls off in an accelerating manner the more the vertical angle increases. This error function is like a bell shape, with the best accuracy when the anemometer is upright, and an accelerating drop in accuracy with tilt toward or away from the wind. The research typically shows that the drop-off follows a cosine curve, with increasingly worse sensitivity to wind speed as the angle increases in equal steps. This kind of response function occurs in all anemometers presently in use in marine environments, and has been documented by Riso National Laboratory—Denmark (2002), and for example the Expert Group Study on Recommended Practices for Wind Turbine testing and Evaluation (1999). The specification sheet for the Thies Anemometer First Class Advanced provides good documentation on its response characteristics, and shows the same drop in accuracy as the anemometer leans away from the wind up to 35 degrees, closely following a cosine curve.
This response function is a problem for anemometers used in sailboats, which may heel at 30 degrees or more when under sail. All types of sailing—recreational, long-distance cruising, and elite racing—requires accurate wind information for navigation. However, there is little awareness of this lack of accuracy in wind sensors when sailing, and no apparent solutions available. Sailors go to great lengths to improve the precision and efficiency of their equipment. But if basic measures of wind speed and wind direction are not accurate whenever a sailboat heels (i.e. most of the time), then tacking calculations and route planning will not be accurate.
Although wind is obviously important for sailboats, and cup anemometers are the most common type on sailboats, the cup anemometer design was made for the roof of the Armagh Observatory in the 19th Century, not for sailboats, which by their nature lean over (or “heel”). Rather than spinning the cups faster when the wind heels the sailboat over on its side, this transfers the force up the axle. A solution is needed that is designed for sailing, so that the cups continue to spin with the same accuracy when the boat is upright or heeling.
A further problem with the state of the art is that there are no mounted, full-featured anemometers available for small sailboats, because these devices are not waterproof and durable enough for the flips that small sailboats sometimes experience in wind gusts. Also, marine electronics have only been for large sailboats, even though mobile devices like smartphones and tablets now have full chartplotting capabilities and are ubiquitous worldwide now. It is easy to have a waterproof container or dry bag for a mobile device, which now support advanced navigation functions, so it would make sense to give small boat sailors the same functions available on large boats.
Most marine anemometers have a further limitation with horizontal arms and surfaces. These make attractive perches for birds. This may damage the wind sensor, especially with the weight of a bird as large as a seagull, crow or eagle. Bird droppings may also interfere with the unit's functioning and solar panels.
A further disadvantage of the state of the art is configuring multiple axes of rotation, for allowing the wind cup and wind direction arrow to spin independently, while also allowing side-to-side movement on a gimbal if there is a need to keep the vane upright. It is tricky to find a way to mount three different bearings and axles in a compact form. One solution is to use a rod-end bearing, which offers rotation and also tilting back and forth. However, although this and other bearings typically allow tilt for misalignment in mechanical components up to 30 degrees, sailboats can heel farther than this. Putting three bearings in a wind vane may also add weight. It is also difficult to find maintenance-free bearings, which would be best for using the vane at the top of a sailboat mast. A method or machine is needed for equally accurate wind sensing with any amount of tilt in the sailboat.
There is also a problem with the standard use of 360-degree potentiometers to provide voltage resistance changes to represent wind direction. These mechanisms have a transition point sometimes referred to as a “dead band”, where resistance must change from lowest resistance to highest resistance, to start the rotation over again. But in this zone, there is no sensitivity, and read-outs may be of wind directions nearby.
A further limitation with the state of the art is that wind direction arrows may also become less accurate when sailboats are heeling over while sailing. When a wind arrow on an anemometer is tilted by 30 to 40 degrees or more, it begins to point vertically, not into the wind. Those skilled in the art will know that the standard procedure for all anemometers is to mount them and calibrate the arrow when the boat is upright, setting the arrow on its axis with the arrow pointing to the front of the boat or to North. But even if the wind direction is constant, the arrow may not aim in the same direction when the boat is heeled over while sailing. The distortion is also a function of wind angle, because a 90-degree wind angle off the beam will not affect the wind arrow direction as the wind arrow leans away, even though a 45 or 135-degree wind angle will. This is not an effect of gravity pulling on the tail of the wind arrow, but simply that the direction of the wind arrow may change as its orientation leans sideways. This needs to be accounted for to obtain accurate wind direction readings, and for the navigator to obtain accurate results for optimal tacks and Tacking Time to Destination. But there seems to be little awareness of this issue, no solutions available, and little research to document it (perhaps because it is more of a problem in sailing than in wind power generation farms).
A further limitation with anemometers commonly used on sailboats is that they need to be calibrated for wind direction. Since boats can move, North is not always in the same direction, so a common procedure is the calibrate the anemometer relative to the bow of the sailboat. Then when the boat is moving and its GPS heading (or compass heading) is known, the wind angle is available, and the wind direction can be derived. Unfortunately, a further disadvantage of existing anemometers is that it is impossible to calibrate them on high-tech rotating masts. Those skilled in the art will know that some modern performance sailboats have a mast that rotates when the sail moves across the boat on port and starboard tacks. But if the mast rotates with the sail, and the anemometer is mounted at the top of the mast, the anemometer cannot be calibrated with the bow of the boat (since the anemometer will rotate back and forth on the mast).
There is also a problem with wiring of anemometers on sailboats. Installing wiring for an anemometer down from the top of a mast of 50 feet or more, through the walls and floor of a sailboat is expensive, difficult and dangerous. Since boats are subject to harsh environmental conditions like tropical sun, and to constant movement, wiring (and even heavy rope) also tends to chafe unexpectedly fast. Installing 50 feet of wiring down the inside of an aluminum mast also adds weight above the boat's center of gravity, and causes annoying noise from the wire banging around inside the long metal hollow mast.
There is a further problem with wiring connections within the anemometer itself. Circuit board electronics have a common problem in marine electronics of all kinds, in that they are exposed to air even if inside a waterproof housing. Air can have moisture in it, which may cause frost or condensation during temperature changes. It would be better if a way could be found to surround the circuit board inside the waterproof housing with dry nitrogen or some other substance to avoid moisture problems in air around the circuit board.
A further problem with installing wiring at the top of a mast is that it is sometimes actually easier to lower all of the rigging and a long mast, than to try to raise someone high above the deck in a “bosun's chair” with power tools, to mount an anemometer. But bringing the mast down is awkward and expensive, and requires a crane for most keelboats. Putting the anemometer on a stern rail is possible, but wind is not as clean there. A better method or machine is needed for getting the wind vane to the top of the mast.
Finally, even if a wireless anemometer is used at the top of the sailboat mast, there are still problems for receiving and displaying the data. What if the user doesn't have a compatible mobile app, or a device that supports apps? There are also limitations if the user has marine electronics like a GPS chartplotter on which they want to display wind data and tacking results, but there is no way to get the wireless signal into the chartplotter.
A machine that could solve these problems would be very useful.